Haven't yet found the parts lists and drawings on the new Tacx HP either. The T1946.50 is the 110 V Fortius isn't it? The part number for the newer interface for the Fortius brake is T1932. Looks a bit different than the old solid blue controller, but works. I had one on my long substituted Fortius and my wife still has one on her Fortius.

I had replaced my old solid blue one on the Fortius with the T1932 because the old controller went on permanent strike. Probably too much sweat intrusion. If that's the issue with your controller, too: mcorn recommended to take it apart and rinse it with a mildly alkaline solution (bit of baking soda in water) and water and letting it air-dry overnight. I read that recommendation too late for my old controller. My Fortius is long gone.

My wife's Fortius started its life as a Cosmos. The Cosmos was a Fortius with a stand-alone controller, it wasn't hooked up to a PC for riding. I finally talked her into getting the T1932 instead and use RLVs on the PC, but she still guards that Cosmos controller as a fall-back position.

It may be worth a thought to not hunt for a new controller for a legacy trainer, but use the money for a newer trainer. A number of folks are upgrading to "Smart" trainers these days and therefore some older non-Smart Genius trainers are on the market. Essentially the Fortius's successor and less legacy than the Fortius. Of course that depends on your PC (the Tacx Trainer Software is more demanding than the old Fortius software) and whether your environment has so much electronic noise that you prefer a wired trainer.

One more thought. You can also look for the T1925 "Flow Upgrade" which is the bundle of the T1932 controller with whatever TTS version was current at the time. You also can look for an i-Flow. (Make sure it's the i-Flow with the T1932 controller and not the Flow with its standalone controller.) The i-Flow was the cheapest trainer using the T1932, and either a used T1925 bundle or a used i-Flow may come cheaper than a new T1932 alone.

Good! There seems to be one more difference between the 240 and 110 V models than the voltage - on our 240 V units, one couldn't detach the cable connecting power unit and brake from the power unit.

One important point is using the correct cable connecting the power unit and the controller. It looks like a telephone cable, but it is a straight-through, not a crossover cable. So no using just any 4-pin cable you may find. Good luck in finding the correct cable then!

The Tacx Trainer Software does support the Fortius trainer. My wife's Fortius is on the most recent version, TTS 4.21. I don't think there is a difference between the 110 and 240 V models in this respect. I don't know, however, whether spending money on upgrading the PC and the software right now is a good idea. There are rumours about changes in the Tacx software environment. They definitely need to find a way to compete with Zwift and I still am flabbergasted they didn't come up with something for this trainer season. On the other hand, no one knows whether any new software will still support the legacy wired trainers.

Another point is that having a separate PC to control the trainer is preferable, in particular if you run other video software - TTS has issues with some other codecs. Choice also depends on how you train. TTS has other VR worlds. There is a way to move old RLVs over to TTS if you use those and there's a world of new RLVs of much higher quality for TTS. No significant changes to the "Catalyst" part of the software. One advantage of using TTS for the Fortius is being able to use ANT devices in parallel - coupling an ANT HR strap provides more stable HR readings than the original analog strap, in particular where you have a lot of electronic noise. So if you are happy with your present sytem, love your VR trainings, put little value on high quality RLVs, have little electronic noise and do video editing, there are some arguments to stay with the Fortius software and a separate, if old, PC.

The only way I know to test in advance whether your trainer still works ok is firing up the Fortius software and try using the trainer.

Thanks for the reply. PC specs aren't an issue - mine's well within TTS range. It burns more watts than I can produce on the bike.

There are a couple of local TACX dealers. They weren't there when I picked up the T1946. If my system won't deal with W7 X32 and the decrepit Fortius drivers I'll see if I can smooze one of them into DXing my T1946 on the TTS stuff. Testing that out later tonight.

Note: W8.1 kicks a spectacular "Kmode Exception Not Handled Error" and BSODS when it sees the device driver. Seems to me I was only running W7 x32 and x64 when I shelved the T1946.